Someone in the thread linked an official announcement in Japanese claiming the ICS update increased battery life by ~50% among other details. I can't find it now though. All I can remember was that it claimed a running time of 30+ hours or so (when using all the gimmicks that jack up battery life including playing low rez mp3 files, no sound enhancements, screen off, etc). I did noticed a considerable improvement in battery life, but haven't timed it myself. Battery life is decent as long as you minimize screen usage and turn on airplane mode.
You can't update from a MAC? what a bummer. Time to hit up a friend's place! ICS is worth the hassle.